Explanation

In Kjeldahl's method, nitrogen present in the compound is converted into ammonia, which is absorbed by a known volume of standard acid.

Given volume of sulfuric acid = 15 mL = 0.015 L Molarity of H₂SO₄ = 1 M

Moles of H₂SO₄ used:

$$ = 1 \times 0.015 = 0.015 \text{ mol} $$

Neutralization reaction:

$$ 2NH_3 + H_2SO_4 \rightarrow (NH_4)_2SO_4 $$

One mole of H₂SO₄ reacts with two moles of NH₃.

Moles of NH₃ evolved:

$$ = 2 \times 0.015 = 0.030 \text{ mol} $$

Each mole of ammonia contains one mole of nitrogen.

Mass of nitrogen:

$$ = 0.030 \times 14 = 0.42 \text{ g} $$

Percentage of nitrogen in the compound:

$$ = \frac{0.42}{1.0} \times 100 = 42\% $$

Hence, the correct answer is 42.

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